The disclosure of Japanese Patent Application No. 2001-239842 filed on Aug. 7, 2001, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a control apparatus and method for a vehicle which has an internal combustion engine such as, for example, a gasoline engine or a diesel engine connected on its output side via a mechanical clutch to a drive train including a transmission and which is equipped with functional devices such as accessories operating on the basis of a torque transmitted from the internal combustion engine.
2. Description of Related Art
As is well known, there have been earnest demands for an improvement of fuel consumption in vehicles. To improve fuel consumption in a vehicle employing an internal combustion engine as a power source, it is desirable that the internal combustion engine be always operated with high efficiency. While power generated by the internal combustion engine is used to cause the vehicle to run, it is also used as power for driving accessories such as, for example, a generator and an air-conditioner. Therefore, it is desirable to operate the internal combustion engine in such a manner as to satisfy requirements regarding a running state of the vehicle and the accessories.
In view of these circumstances, for example, according to JP-A-8-135778, a true value of running load is calculated by subtracting a correction amount corresponding to loads of accessories such as an air-conditioner and an alternator from a depression stroke of an accelerator pedal indicating a required drive amount for causing a vehicle to run, and a timing for making a gear shift or engaging a lockup clutch is determined on the basis of the corrected running load. The aforementioned technology ensures that a timing for upshift or lockup does not shift to the side of higher speeds, and thus makes it possible to improve fuel consumption or emission properties.
The aforementioned technology is designed to prevent an engine from being operated at an unnecessarily high speed when the vehicle runs on the basis of an output from the engine. On the other hand, a so-called fuel-cut operation is known as a technique for improving fuel consumption in a vehicle employing an internal combustion engine as a power source. When the internal combustion engine runs at a speed equal to or higher than a predetermined speed during slowdown of the vehicle, the fuel-cut operation is performed by stopping supply of fuel to the engine on the condition that an accelerator pedal is released completely.
The fuel-cut operation as mentioned herein can be performed at a speed equal to or higher than a speed at which the internal combustion engine can start running autonomously again in response to resumption of the supply of fuel. Hence, if the vehicle is equipped with the aforementioned lockup clutch, the lockup clutch remains engaged so that the speed of the internal combustion engine is increased to the highest possible speed by an inertia force applied to the vehicle in a running state. On the other hand, the lockup clutch mechanically and directly couples the internal combustion engine with the drive train including the transmission connected to the output side of the internal combustion engine. If the lockup clutch is engaged, namely, if the lockup clutch is in a lockup state, oscillation of the internal combustion engine is likely to be transmitted to a body of the vehicle via the drive train. Low-frequency oscillation is sensed as a booming noise or the like and thus constitutes a factor causing deterioration in driving comfort. For this reason, the control according to this technology is designed such that the lockup clutch that is engaged during slowdown of the vehicle is released if the engine speed falls to a predetermined speed, and thereby prevents oscillation of the internal combustion engine from being transmitted to the vehicle body. In this case, since the speed of the internal combustion engine falls because of release of the lockup clutch, the fuel-cut operation is stopped and the supply of fuel to the internal combustion engine is resumed.
As described above, the lockup clutch is released during slowdown of the vehicle as a countermeasure against deterioration in driving comfort resulting from oscillation. On the other hand, if the internal combustion engine drives accessories such as an air-conditioner and an alternator, the load applied to the internal combustion engine has been increased by an amount corresponding to loads caused by the accessories. Therefore, the internal combustion engine oscillates more violently, and oscillation or booming noise resulting therefrom tends to cause deterioration in driving comfort. That is, if the internal combustion engine drives the accessories, oscillation of the internal combustion engine tends to occur due to an increased load. As a result, it is desirable to release the lockup clutch when the internal combustion engine runs at a relatively high speed. In other words, a disadvantage arises in improving fuel consumption.
There is no technology that attempts to tackle this problem. Although the aforementioned publication refers to technical details about the timing for lockup, the timing for releasing the lockup clutch is not addressed.
It is one object of the invention to provide a control apparatus and method capable of improving fuel consumption in a vehicle equipped with an internal combustion engine.
To achieve the above and/or other objects, the control apparatus and method according to one aspect of the invention reduces loads resulting from functional devices such as accessories operated by power transmitted from an internal combustion engine when a vehicle slows down with the internal combustion engine mechanically coupled on its output side to a drive train by means of a clutch so as to reduce a load applied to the internal combustion engine. The internal combustion engine typically is connected via a mechanical clutch to a drive train including a transmission. The vehicle includes one or more functional device(s) operated by a torque generated by the internal combustion engine. The control apparatus and method controls a load applied by the functional device on the internal combustion engine when the mechanical clutch is in an engaged state during deceleration of the vehicle and a speed of the internal combustion engine is lower than a predetermined value such that the load is reduced to a first value lower than a second value of the load applied to the engine when the speed of the internal combustion engine is equal to or higher than the predetermined value.
According to the aforementioned aspect, the mechanical clutch directly couples the internal combustion engine and the drive train with each other when the vehicle slows down, and the internal combustion engine drives the functional devices while this state is maintained. If the speed of the internal combustion engine gradually falls during slowdown of the vehicle and then becomes equal to or lower than a predetermined speed, loads applied to the internal combustion engine by the functional devices are made lower than the load applied before. The load applied to the internal combustion engine is reduced, and oscillation generated in the internal combustion engine is suppressed. Even if the mechanical clutch remains engaged, factors causing deterioration in driving comfort such as booming noise hardly arise. Thus, the mechanical clutch can be left engaged until the speed of the internal combustion engine reaches a relatively low speed. In other words, the period in which the mechanical clutch is engaged to maintain the speed of the internal combustion engine at or above a speed corresponding to resumption of the supply of fuel can be extended. Accordingly, it becomes possible to achieve improvement in fuel consumption.
According to another aspect of the invention, a function compensating device can be provided to compensate for a functional deterioration caused by reduction of the load of the functional device on the internal combustion engine.
According to the aforementioned aspect, if the load(s) applied to the internal combustion engine by the functional device(s) is/are reduced, namely, if the operational state(s) of the functional device(s) deteriorate, the function compensating device compensates for a loss in the functions of the functional devices. Therefore, the vehicle can be maintained in the same operational or running state as before.
According to another aspect of the invention, when the functional deterioration of the functional device is not compensated for by the function compensating device, the speed of the internal combustion engine at which a torque capacity of the mechanical clutch is reduced can be set to a third value higher than the first value that is set when the functional deterioration is compensated for by the function compensating device.
According to this aspect of the invention, if the function compensating device cannot compensate for a loss in the functions of the functional device(s), the speed corresponding to reduction of the torque capacity of the mechanical clutch becomes higher during slowdown of the vehicle. In the case where the mechanical clutch is engaged to increase the speed of the internal combustion engine and where the supply of fuel to the internal combustion engine is stopped as a result, the supply of fuel is resumed when the internal combustion engine runs at a relatively high speed. Consequently, the internal combustion engine runs autonomously, and the functional device(s) is/are driven by the output from the internal combustion engine, whereby the functional devices are guaranteed to operate properly. Therefore, the vehicle is maintained in the same operational or running state as before.